https://arscna.org/wp-content/plugins/bmlt-tabbed-map/public/js/leaflet.spin.js?ver=1.2.1

1L.SpinMapMixin = {
2    spin: function (state, options) {
3        if (!!state) {
4            // start spinning !
5            if (!this._spinner) {
6                this._spinner = new Spinner(options).spin(this._container);
7                this._spinning = 0;
8            }
9            this._spinning++;
10        }
11        else {
12            this._spinning--;
13            if (this._spinning <= 0) {
14                // end spinning !
15                if (this._spinner) {
16                    this._spinner.stop();
17                    this._spinner = null;
18                }
19            }
20        }
21    }
22};
23
24L.Map.include(L.SpinMapMixin);
25
26L.Map.addInitHook(function () {
27    this.on('layeradd', function (e) {
28        // If added layer is currently loading, spin !
29        if (e.layer.loading) this.spin(true);
30        if (typeof e.layer.on != 'function') return;
31        e.layer.on('data:loading', function () { this.spin(true); }, this);
32        e.layer.on('data:loaded',  function () { this.spin(false); }, this);
33    }, this);
34    this.on('layerremove', function (e) {
35        // Clean-up
36        if (e.layer.loading) this.spin(false);
37        if (typeof e.layer.on != 'function') return;
38        e.layer.off('data:loaded');
39        e.layer.off('data:loading');
40    }, this);
41});